I have a home that was built in 1961. It has an attached two car garage with an unfinished ceiling and attic space. The former owner had laid some old mismatched pieces of plywood over the ceiling joists for storage. I would like to finish off the ceiling with sheetrock and put down a subfloor on top of the joists for storage that would be accessed through a pull down attic ladder.
The garage is 20' wide and 26' deep on the left side of garage and 21' deep on the right as the entry way to the house is on the the back side of the right half of the garage.
The ceiling joists are 2x6's, 32" o.c. and run 21' from the front wall to the back wall on the right side and 21' from the front wall to a doubled up 2x4's extending from the back wall on the right side of garage over to the left side wall of garage. The additional area in the back left side of garage has no ceiling joists and is open up to the rafters.
The rafters are 2x6's, 16" o.c. and the ceiling joists are tied to them in the center of the garage roof line (13' from the front of garage) by 2x4's.
I have walked on these (I am 250 lbs.) and they seem pretty sturdy other than a bit of side to side wobble since there is no blocking between the joists.
I know that the joist spacing of 32" o.c. is not sufficient to properly support 5/8 rock and was planning on adding 2x6 every 16" o.c. for this.
However, with such a long span will 2x6's every 16" o.c. be strong enough to put down 1/2" or 3/4" plywood sheets for storage safely? Would not necessarily be storing anything real heavy but would need to walk around the garage attic space to access stored items.
Additionally, is the doubled up 2x4's strong enough to support the ends of the joists for the 7 foot section on the left side of garage?
Please refer to pictures for details.

sunthas

01-03-2009 11:53 PM

I moved into my house with a completely sheetrocked garage with some OSB put down in the garage attic to use as storage, just a access hole in the ceiling which I've since replaced with an aluminum pull-down ladder.

I've noticed that the previous owner didn't beef up the joists enough to handle the walking around, holding the drywall doesn't seem to be too difficult. They did add extra 2x4s to double the thickness of the ceiling but I don't think they sistered them correctly to the joists to stiffen the joists. So when you walk around on the OSB in the attic the ceiling flexes and the drywall seams crack. At some point if we are in this house long enough, I'll pull up the attic floor and redo it correctly.

DIY KEN

01-04-2009 12:23 AM

That is exactly why I want to know ahead of time what I will need to do to make sure it is done right.

I know that I could just run furring strips and sheet rock as is and not use the attic for storage. However, there is a lot of space up there that I would like to be able to use for storage as well as adding value to the home if I should sell sometime in the future. Of course it is only going to add value to myself and any future owners of the home if it is done correctly.

Good luck with your future redo and for the time being, be very careful as it sounds like you or anything heavy stored in that attic space has the potential to come crashing down through the garage ceiling.

kelukens

01-04-2009 03:06 PM

Some suggestions for you

You're right to be concerned about the 32" spacing. Your idea to add joists to make 16" centers is a must, and at a minimum I would add 2x4 vertical supports to the new joists just like the existing supports, and if you would feel safer, you could add a shorter 2x4 at an angle where the joists rest on the wall plate to create a custom truss effect. The more you make it act like a truss, the more weight you can store Be sure when you add your ladder steps to frame it with 2x6's between the joists for added support.:)

DIY KEN

01-04-2009 03:53 PM

Thank you for your feedback.

Do you know any formulas that I could use to determine what the weight capacity for storage would be with the 2x6's running the 21' spans with 16" o.c. and the addition of the vertical supports that you propose?

markus

01-04-2009 04:07 PM

Quote:

Originally Posted by DIY KEN
(Post 206806)

Thank you for your feedback.

Do you know any formulas that I could use to determine what the weight capacity for storage would be with the 2x6's running the 21' spans with 16" o.c. and the addition of the vertical supports that you propose?

DIY KEN, check out the following calculator. You may have differing requirements in your area, I usually over-build everything so there's no question.

I saw the reply from Marcus with the calculator; I will use it for the loft I'm planning to build. Remember that your span will be somewhat shortened because of your center support. I would not cut the span in half for your calculations, but your span would be close to half. (In my opinion)

Good luck with your project,

Ken

Baron

01-06-2009 05:57 PM

2x6s can only span barely 14 feet for a 20psf load (Light Storage) at 16"' OC.
So you need to do something to carry the load differently to get adequate support

I would add full length 2x6s at 16 OC and remove the center braces and make a type of W truss with 1x8 spruce every other joist/rafter that would give you the entire center for storage and little to non on the 1/3 remaining ends. Nail and glue the boards with a minimum of 5 8d nails. (Boards are better than 2x6s at this point for the truss material)

The common math to make the truss would be at the beginning of the W it is attached at the 1/2 point of a rafter then angle down to 1/3 of joist then back up to ridge and repeat on the opposite side to complete the W. You wouldn't have to worry too much about weight deflection being transferred to the roof.

I think you could get about 7 feet of middle storage with this method.
You also would not be adding weight to the ridge pole.